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Overpowering cabinets

Discussion in 'Amps and Cabs [BG]' started by nil, Apr 4, 2002.

  1. How safe is it to run a cabinet rated lower than the output of the amp?

    For example, could a 500w@4ohm (continuous) amp run a 300w@4ohm (continuous) cabinet without blowing it up? Would it be OK as long as the amp didn't clip?
  2. As long as you don't push the volume, it'll be fine. Keep in mind, most amps rated at 500w aren't actually rated at attainable watts. If you went to the 500w, you would clip like crazy. Tube amps are rated with attainable watts, as is the new DB750 by Aguilar.
  3. Cool...just been thinking of getting a new 4x10 that I can bridge my Eden (800w) into.
    The best power handling (for price and availability) i've found is only 600w though, so i'd be 200w over.
    The Eden does have a good output limiter though, which could/should/might save me, but i'm assuming that even with that kicking in, i'd still be pushing a full 800w outta the back (i've scoped one side and under full load with the limiter active it's pushing a smidgeon under 400w).
  4. Well no, you wouldn't be pushing a full 800w unless you turn the volume knob all the way to the max. The watts are controled by the volume knob. And i'm sure you won't need to crank it to any sort of rediculously extreme level to be loud enough.
  5. If the output limiter is kicking in, doesn't that mean that the headroom has been reached?

    And if an amp has an output limiter, does that limit the continuous output, or the peak?

    I guess i'm just afraid of blowing up a cabinet inadvertently...(like, would a heavy slap causing the amp to peak a bit push the cabinet over the edge and BRRRAAAP!)
  6. Captain Awesome

    Captain Awesome

    Apr 2, 2001
    Nope, the watts are controlled by how hard you're playing and how hot your signal is to begin with. The volume control just controls the overall gain, whether the amp's output circuitry can keep up with it or not.
  7. Well i was just trying to get a basic point off, i wasn't really trying to get into it fully.
  8. You'll be fine. Here's what JBL has to say about it and they might know a thing or two on the subject...

    How do I choose the right amplifier power for my speaker system?

    Ideally you should pick an amplifier that can deliver power equal to twice the speaker's continuous IEC power rating. This means that a speaker with a "nominal impedance" of 8 ohms and a continuous IEC power rating of 350 watts will require an amplifier that can produce 700 watts into an 8 ohm load. For a stereo pair of speakers, the amplifier should be rated at 700 watts per channel into 8 ohms.
    A quality professional loudspeaker can handle transient peaks in excess of its rated power if the amplifier can deliver those peaks without distortion. Using an amp with some extra "headroom" will help assure that only clean, undistorted power gets to your speakers. Some professional amplifiers are designed so they have additional headroom. These amps can cleanly reproduce transient peaks that exceed the amplifier's rated power. In this case select a model with an output power rating equal to the continuous IEC power rating of the speaker.
  9. DaveB


    Mar 29, 2000
    Toronto Ontario
    Mudbass - Good post!!!
  10. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Commercial User

    Jul 3, 2001
    Santa Ana, Calif.
    Former Technical Communications Developer, QSC Audio
    A speaker's continuous power rating is generally related to how much heat it can dissipate, because most of the power going into its voice coil converts to heat, which gets transferred to the magnet and the frame and then into the air in the cabinet. If you keep putting power into the voice coil faster than the resulting heat can escape, its temperature will rise quickly, and at some point it's likely to burn out the coil wire or melt the adhesives that hold it together. Either way, it's shot.

    That's continuous power. The speaker can handle short-term peaks that are much higher than the continuous power rating. That's good, because music has a lot of peaks, like your finger snapping a string, that are a lot higher than the average level. If you burn CDs or rip MP3s, a lot of the software will show a graph of the signal level of the recording versus time; you'll see those peaks. You need the amp powerful enough to handle those without clipping. Imagine the signal levels averaged out over time. You need the speaker strong enough to handle that power.

    So you can safely use an amp that's reasonably more powerful than the speaker if you avoid clipping. For example, I use a PLX 1602 (1000 watts in bridged mono at 8 ohms) to drive an 8-ohm cabinet rated at 200 watts continuous. In four years I've seen the clip LEDs flash only a couple times, and I haven't blown a speaker.

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